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In-Reply-To: <990481.1782266035@sss.pgh.pa.us>
From: Amit Langote <amitlangote09@gmail.com>
Date: Wed, 24 Jun 2026 12:50:28 +0900
Message-ID: 
 <CA+HiwqFKFSSGg7Xygw6r3WK+HKOt6FXLTBuVOyFEH76_To9U8g@mail.gmail.com>
Subject: Re: BUG #19484: Segmentation fault triggered by FDW
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Etsuro Fujita <etsuro.fujita@gmail.com>,
 Matheus Alcantara <matheusssilv97@gmail.com>,
	Ayush Tiwari <ayushtiwari.slg01@gmail.com>,
 Rafia Sabih <rafia.pghackers@gmail.com>,
	798604270@qq.com, pgsql-bugs@lists.postgresql.org,
	Amit Langote <amitlan@postgresql.org>
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On Wed, Jun 24, 2026 at 10:53=E2=80=AFAM Tom Lane <tgl@sss.pgh.pa.us> wrote=
:
> Amit Langote <amitlangote09@gmail.com> writes:
> > crake is now red on REL_18:
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=3Dcrake&dt=3D20=
26-06-24%2000%3A02%3A03
>
> > It reports sizeof(ModifyTableState) grew by 8 bytes.
>
> > That=E2=80=99s from adding mt_fdwPrivLists at the end of the struct. Pl=
acing it
> > last keeps existing field offsets stable, which is what extensions read=
ing
> > the node rely on, but it does grow the struct, which is what the checke=
r
> > flags. I believe we=E2=80=99ve added trailing struct members in back br=
anches
> > before for exactly this reason. Is a flagged sizeof increase acceptable
> > here under that precedent, or do we now want to avoid any flagged ABI
> > change on a back branch?
>
> I don't believe that the addition of ABI checking was meant to change
> our back-patching policies, just to make sure we don't make
> unintentional ABI changes.  As you say, we've added trailing fields
> before.  The critical question is whether it's likely that any
> extensions create their own ModifyTableState nodes (and might make
> them too small and/or fail to fill the new field correctly).
>
> I was about to say that that seems unlikely to me, but a check of
> Debian Code Search immediately found pg_rewrite doing it.  So yeah,
> looks like we'd better adopt the no-ABI-break solution.

Ah, ok, will post the patch to do so in the REL_18_STABLE branch.

Thanks for the comment.

--=20
Thanks, Amit Langote